For a long time, scientists considered fungi to be members of the plant kingdom because they have obvious similarities with plants. Both fungi and plants are immobile, have cell walls, and grow in soil. Some fungi, such as
lichens
, even look like plants (see
Figure
below
).

Moss (Plant) and Lichen Growing on Tree Bark. Both fungi and moss are growing on this tree. Can you tell them apart?

The Kingdom Fungi

Today, fungi are no longer classified as plants. We now know that they have unique physical, chemical, and genetic traits that set them apart from plants and other eukaryotes. For example, the cell walls of fungi are made of
chitin
, not cellulose. Also, fungi absorb nutrients from other organisms, whereas plants make their own food. These are just a few of the reasons fungi are now placed in their own kingdom.

Fungal Phyla

Classification of fungi below the level of the kingdom is controversial. There is no single, widely-accepted system of fungal classification. Most classifications include several phyla (the next major taxon below the kingdom). Three of the most common phyla are compared in
Table
below
.

Phylum

Description

Example

Zygomycota

mainly terrestrial, live in soil and compost and on foods such as bread

black bread mold

Basidiomycota

have many different shapes, considerable variation exists even within species

button mushrooms

Ascomycota

found in all terrestrial ecosystems world-wide, even in Antarctica, often involved in symbiotic relationships

baker’s yeast

Summary

Fungi used to be classified as plants. Now, they are known to have unique traits that set them apart from plants. For example, fungal cell walls contain chitin, not cellulose, and fungi absorb food rather than make their own.

Below the level of the kingdom, classification of fungi is controversial.